1. Field of the Invention
The present invention relates to a display drive device which drives a display panel based on display data, a display device having the display drive device, and a method for driving a display panel.
2. Description of the Related Art
In an active matrix type liquid crystal display device, a plurality of scan lines and a plurality of signal lines are laid out on a liquid crystal display panel in such a manner as to be orthogonal to one another, and display pixels are formed in the vicinity of individual intersections. Each display pixel has a liquid crystal capacitor where a liquid crystal is filled between a pixel electrode, connected to the signal line and the scan line via a TFT (Thin Film Transistor), and a common electrode.
In such a liquid crystal display device, as scan signals (gate pulses) are sequentially applied to individual scan lines by a scan driver so as to be a selected state, the TFTs of corresponding display pixels become an ON state. A display signal voltage applied to each signal line by a signal driver is then applied to the pixel electrode through the TFT. Accordingly, a voltage difference between the display signal voltage and a common signal voltage VCOM applied to the common electrode is applied to a corresponding liquid crystal capacitor, charged in the liquid crystal capacitor, so that orientation states of liquid crystal molecules are controlled. Therefore, a desired image is displayed on the liquid crystal display panel.
FIG. 13 is a diagram illustrating an example of wirings of drivers and a display pixel section in the liquid crystal display device.
As illustrated in FIG. 13, a liquid crystal display device 9 is formed on, for example, a glass substrate 90. The liquid crystal display device 9 has a display pixel section 91 in which display pixels are arrayed, a signal driver 92 and a scan driver 94. Because of a demand of narrowing the right and left width of the glass substrate 90 without changing the size of the display pixel section 91, the signal driver 92 and the scan driver 94 arranged with each other may be disposed on the glass substrate 9 only at one edge side of the display pixel section 91 as illustrated in FIG. 13. At this time, a plurality of signal lines 93 and a scan line 95 are wired in such a way that both the signal driver 92 and scan driver 94 are connected to the display pixel section 91. At this time, an interwiring capacitor as a parasitic capacitor is provided between each signal line 93 and each scan line 95.
In such an arrangement, as the number of signal lines 93 increases, or a clearance between the signal driver 92 and the display pixel section 91 becomes narrow, a portion where the density of the wirings of the signal lines 93 becomes high is created. In FIG. 13, the signal driver 92 is disposed on the left side, and the scan driver 94 is disposed on the right side. Therefore, the wirings of the signal lines 93 becomes longer in wiring length and narrower in pitch (interval) rightward. That is, a region B has a longer wiring length and a narrower pitch than a region A. At this time, the interwiring capacitor created between the signal lines 93 in the region B becomes larger than the interwiring capacitor created between the signal lines 93 in the region A.
FIG. 14A is an example of a cross-sectional view of the wiring portions of the signal lines 93 in the liquid crystal display device 9 illustrated in FIG. 13, and FIG. 14B is an equivalent circuit diagram thereof.
As illustrated in FIG. 14A, the wiring portions of the signal lines 93 employ a structure that, for example, the linear signal lines 93 made of a metal, such as Cr or Al are formed on an SiN nitride film 96 formed as an insulating film on the glass substrate 90 at intervals, and an SiN nitride film 97 is formed thereover, so that a space between signal lines 93 is insulated, and the upper portion is covered by a seal material 98.
That is, as illustrated in FIG. 14B, the interwiring capacitance of the signal line 93 is the combined capacitance of a capacitance Cx originated from the glass substrate 90, a capacitance Cy originated from the SiN nitride films 96, 97, and a capacitance Cz originated from the seal material 98. The longer the wiring length of the signal line 93 is or the narrower the pitch is, the larger the interwiring capacitance becomes. That is, the higher the density of the signal lines 93 becomes and the longer the wiring length becomes, the larger the interwiring capacitance of the signal line 93 becomes.
Recently, higher definition of the liquid crystal display panel is remarkable, and an increment in signal line number originated from the higher definition raises a problem that the electrical power consumption of the signal driver increases and the cost increases. As a method of driving and controlling the liquid crystal display panel to prevent the problem, a scheme of grouping a plurality of signal lines into predetermined numbers of signal lines (for example, three lines), sequentially selecting each predetermined number thereof, and driving the panel in a time sharing manner may be employed.
In a case where such time-shared driving is applied to the liquid crystal display device 9 having the arrangement as illustrated in FIG. 13, the voltage of the signal line 93 in a non-selected state may change when the display signal voltage is applied depending on the interwiring capacitor.